As integrated circuit processing continues to advance, effort is made to increase the capacity and reduce the size of integrated circuits. While traditional complementary metal-oxide semiconductor (CMOS) scaling processes improve signal propagation speed, scaling from current manufacturing and chip-design technologies is becoming more difficult and costly, in part because of power-density constraints, and in part because interconnects do not become faster with faster transistors. Three-dimensional (3D) integrated circuits (ICs) address the scaling challenge by stacking 2D die and connecting them in the 3rd dimension using wafer bonding. Among other benefits, the use of 3D ICs enables speeding up communication between layered die, compared to a planar layout.
Typical process defects in the wafer bonding technology normally include an open defect and a short defect of the wafer bonding paths. Finding these defects is very challenging in current 3D IC products, especially at the development stage. It is very difficult to find the exact locations of process defects in the wafer bonding products, due to the large number of bonding paths. While an X-ray scan could be done for a large number of bonding paths, it would take a significant amount of time to find the exact location of the failure. Generally, the number of bonding paths in one daisy chain structure may be a few hundred. If the structure has failed, it would take a significant time to scan the chain, where each bonding path in the structure would have to be carefully scanned by x-ray. A chain with the small number of bonding paths can be placed, but just a few structures can be scanned because of the limited number of probe pads. Finding a root cause of failures and providing feedback to an IC fabrication group as soon as possible can be significant in the manufacture of ICs.
Accordingly, circuits and methods that enable testing bond connections between wafers having a first and second die and between a first and second die in an integrated circuit device are beneficial.